Eicosapentaenoic acid (EPA hereafter) and docosahexaenoic acid (DHA hereafter) are n-3 polyunsaturated fatty acids (PUFA hereafter) having a variety of biological effects, and are used as medical products, health food products, food product materials, and the like. EPA ethyl ester is used as a therapeutic agent for arteriosclerosis and hyperlipidemia, and beverages to which fish oil containing EPA and DHA has been added have been approved as a food for specified health uses. Furthermore, the demand for these fatty acids as a supplement is very high in Japan and other countries.
PUFAs have many double bonds and are therefore very unstable to oxidation. Consequently, that an enzyme reaction that proceeds under mild conditions at room temperature is very desirable for the steps involved in producing PUFA-containing oils.
There are lipase products for industrial use that are obtained from primarily microorganisms and that have the property of hardly reacting with PUFAs. PUFA-enriched oils and fats can be produced using lipases having such a property by emphasizing liberation and removal of fatty acids having few carbons. For instance, a method is disclosed whereby DHA-enriched oils and fats are produced by hydrolysis of tuna oil using Candida cylindoracea lipase and then removal of the free fatty acids (Patent Reference 1).
It is known that water has an important effect on enzyme activation for enzyme reactions in an organic solvent (non-Patent Reference 1). It is reported that when a PUFA is concentrated from cod lever oil using alcoholysis, which is a reaction wherein the fatty acids are severed from glycerides by exposure to an alcohol, the addition of water promotes the lipase reaction (Non-Patent Reference 2). On the other hand, it is disclosed that alcoholysis of oils and fats proceeds under virtually anhydrous conditions with certain lipases. Nevertheless, the amount of lipase used must be very high at 10% the amount of oil, and the lipase must be immobilized in order to improve productivity (Patent Reference 2).
A method is cited in Patent Reference 3 wherein an alkali salt is used when oils and fats containing long-chain polyunsaturated fatty acids as constituent fatty acids are hydrolyzed by a lipase having positions 1 and 3 specificity.    Patent Reference 1 JP (Publication of Unexamined Patent) 58-165796    Patent Reference 2 JP (National Publication) 9-510091    Patent Reference 3 JP (Publication of Unexamined Patent) 3-108489    Non-Patent Reference 1 J. S. Dordick, “Enzymatic catalysis in monophasic organic solvents,” Enzyme Microb. Technol., 1989, 11, Apr., 194-211.    Non-Patent Reference 2 L. Zui and O. P Ward, “Lipase-catalyzed alcoholysis to concentrate the n-3 polyunsaturated fatty acids of cod liver oil,” Enzyme Microb. Technol., 1993, 15, Jul., 601-606.